NPR:

When you step outside after a big rainstorm and take a deep whiff of that fresh, earthy smell, you’re mostly smelling a chemical called geosmin.

It’s a byproduct of bacteria and fungi. And something about rain lofts the chemical — and sometimes the organisms themselves — into the air, a process that not only helps release that earthy smell but may, in very rare conditions, spread diseases.

Somehow raindrops launch tiny living things off the ground.

This is a lot more interesting than it had any right to be.